I just noticed a patch of red, very slightly raised on my 4 1/2 month old's leg. she has no fever, but the spot itself feels warmer than the rest.

Have it checked. : The fact that the red patch just appeared and feels warmer suggests the beginning of an infection or a bite that may have occurred there. U may want to observe it for 12-24 hours if the baby is otherwise fine and feeding well with no fever. If the redness becomes larger and painful or the baby appears ill u shod see doctor right away.